It has been determined by us and others that several of the parvoviruses interfere with viral oncogenesis both in vivo and in vitro. The possible role of these ubiquitous agents in cancer resistance has encouraged us to study the phenomenon in detail. We hope to define the spectrum of interference between certain parvoviruses, in particular H-1 virus originally isolated from human tissue, and various oncogenic agents (viral and chemical) which may prove relevant to human malignancy. The biological interplay between H-1 virus and these transforming agents, some of which act as "helpers," will be explored in productive and non-productive host cell infections. The molecular basis of the interference with malignant transformation, and "helper" virus replication will be sought through an understanding of the molecular biology of H-1 replication. Our growing bank of conditional lethal mutants of H-1 virus will be an important tool for this. The simplicity of H-1 virus and its biochemical dependence on host cell replicative machinery has proved to be more specific than at first realized; this makes the virus a valuable tool for probing many aspects of host cell function. An important aspect of parvovirus biology appears to be latency, and tissue culture and animal models for this will continue to be examined for the mechanism of this phenomenon.